A century ago, Einstein formulated his elegant and elaborate theory of General Relativity,
which has so far withstood a multitude of empirical tests with remarkable success …

After a decade and a half of research motivated by the accelerating universe, theory and
experiment have reached a certain level of maturity. The development of theoretical models …

The dawn of the twenty-first century came with very positive prospects for gravity, cosmology,
and astrophysics. Technological progress made it possible for cosmology to enter to its …

We review recent progress in massive gravity. We start by showing how different theories of
massive gravity emerge from a higher-dimensional theory of general relativity, leading to the …

We review recent progress in the construction of modified gravity models as alternatives to
dark energy as well as the development of cosmological tests of gravity. Einstein's theory of …

A bstract Theories of massive gravity inevitably include an auxiliary reference metric.
Generically, they also contain an inconsistency known as the Boulware-Deser ghost …

This review is dedicated to recent progress in the field of classical, interacting, massive spin-
2 theories, with a focus on ghost-free bimetric theory. We will outline its history and its …

The direct detection of gravitational waves (GWs) from merging binary black holes and
neutron stars marks the beginning of a new era in gravitational physics, and it brings forth …

A bstract We discuss a consistent theory for a self-interacting vector field, breaking an
Abelian symmetry in such a way to obtain an interesting behavior for its longitudinal …

We make precise the heretofore ambiguous statement that anisotropic stress is a sign of a
modification of gravity. We show that in cosmological solutions of very general classes of …